Method of metal plating with a group iv-b organometallic compound



United States Patent 3,061,465 METHOD OF METAL PLATING WITH A GROUP IV-B ORGANOMETALLIC COMPOUND Vello Norman and Thomas P. Whaley, Baton Rouge, La., assignors to Ethyl Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed Oct. 9, 1959, Ser. No. 845,307 11 Claims. (Cl. 117107) This invention relates to a process for plating group IVB metals of the periodic chart of the elements on appropriate substrates by decomposition of organornetallic compounds of such metals.

A simplified flow diagram of the process of this invention is as follows:

Substrate Heat to decomposition temperature of a dicyclopentadienyl group IVB transition metal coordination compound Contact heated substrate with vapors of the above compound Cool In the past, processes for the preparation of a group IVB metal plateparticularly titanium and zirconium p1ateshave been limited to impractical high temperature processes. Illustrative of these high temperature prior art processes are thermal decomposition of titanium or zirconium iodides at 1200 to 1500 C. and hydrogen reduction of titanium tetrachloride and titanium tetrabromide at 1100 to 1400 C.

Plates produced by prior art reduction methods are unsatisfactory for two major reasons. The first of these is that the resultant metal plate is of poor quality due to hydrogen embrittlernent. It is well known that titanium and zirconium are particularly susceptible to hydrogen absorption and this results in the preparation of poor quality hydrogen embrittled metal plates. The second deficiency is that metal plates produced by these prior art methods have poor adherence to the surface on which the metal is plated.

A further problem accompanying prior art processes is the necessity for excessively high temperatures. Furthermore, the plating agents utilized in these prior art processes, (e.g., iodides or bromides of titanium or zirconium) are extremely reactive and, therefore, the use of such high temperatures lends itself to embrittlement of the resultant plate by non-metallic impurities such as oxygen, nitrogen and carbon.

In addition to the above methods, electroplating from fused salt baths has been employed as a technique for producing group IVB metal plates, particularly titanium plates. However, one of the foremost problems relative to this technique is that the plate is deposited thinly and unevenly, or dendritically. Thus, in short, there is no known satisfactory process for producing group IVB metal plates.

Titanium and zirconium metal plates are highly desirable because of their high corrosion resistance and good temperature stability characteristics. Carbides of these metals are also highly desirable, since these materials are extremely hard, high temperature resistant compounds. Heretofore, in producing coatings of hard carbides, it has been necessary to employ temperatures of about Patented Oct. 30, 1962 1200 C. in a reduction process utilizing a mixture of the metal halide, hydrogen and hydrocarbons.

In view of the foregoing, the novelty and great importance of the instant invention becomes clear. For the first time, employing the process of this invention, it is possible to produce-at temperatures significantly below those described above-a well-adhering, pure group IVB metal plate. Furthermore, by a simple variation in the process, it is possible to produce the carbide of the corresponding metalssaid carbide being of excellent characteristics and well-adhering to the substrate upon which it is coated. To the best of our knowledge, this is the first time that such plating processes have been employed in providing group IVB metal plates.

It is, therefore, an object of this invention to provide a process for the preparation of group IV-B metal plates. It is a further object of this invention to produce a welladhering, excellent group 1 IVB metal plate. A still further object of this invention is to produce a group IV- B carbide coating which has good adherence to the substrate upon which deposited.

These and other objects are accomplished in accordance with this invention by providing a process for plating a substrate with a group IVB transition metal by the decomposition of a dicyclopentadienyl group IVB transition metal coordination compound in contact with said substrate. (The group IVB transition metals are titanium, zirconium and hafnium, e.g. see the periodic chart of the elements, Fisher Scientific Company, 1955.)

By the term cyclopentadienyl, which is a substituent in the aforementioned coordination compound, is included substituted cyclopentadienyl groups. The cyclopentadienyl moiety, therefore, includes alkyl and aryl substituted cyclopentadienyl groups as well as indenyl and fluorenyl derivativesincluding substituted indenyl and fluorenyl derivatives. erably includes hydrocarbon cyclopentadienyl groups containing 5 to about 17 carbon atoms. 7

Alternatively the dicyclopentadienyl group IVB coordination compounds of this invention can be defined as dihydrocarbon cyclomatic group IVB coordination compounds. The term cyclomatic hydrocarbon includes cyclomatic hydrocarbon radicals having from about 5 to about 17 or more carbon atoms and embodying a group of 5 carbons having the configuration found in cyclopentadiene. Such cyclomatic hydrocarbon group IVB coordination compounds are further characterized in that the cyclomatic hydrocarbon radical is bonded to the group IVB metal by carbon to carbon bonds, through the carbons of the cyclopentadienyl group contained therein.

each other, involved in covalent or coordinate-covalent bonding with the metal atom, at has a value of 0 to 4- and usually 0 to 2. These group IVB coordination compounds will be more fully defined hereinafter.

By decomposition, as used herein, is meant any method feasible for decomposing a cyclopentadienyl IVB transition metal coordination compound. Thus, the term includes decomposition by ultrasonic frequency and decomposition by ultraviolet irradiation, as Well as thermal decomposition. Thermal decomposition is a preferred mode of carrying out the invention.

The term cyclopentadienyl pref- Therefore, within the scope of this invention, is a process for plating a subtrate with a group IVB transition metal comprising heating the substrate to be plated to a temperature above the decomposition temperature of a cyclopentadienyl gr-oup IV-B transition metal coordination compound, and thereafter contacting said coordination compound with said heated substrate.

Examples of the cyclopentadienyl group IV-B transition metal coordination compounds employed in this invention are: dicyclopentadienyl titanium dichloride, dicyclopentadienyl zirconium dichloride, dicyclopentadienyl titanium, dicyclopentadienyl zirconium, dicyclopentadienyl titanium chloride, dicyclopentadienyl titanium bromide, dicyclopentadienyl zirconium chloride, dicyclopentadienyl titanium dicarbonyl, dicyclopentadienyl titanium diphenyl, bis-(methyl cyclopentadienyl)titanium dichloride, bis-indenyl titanium dichloride, bis-fluorenyl zirconium dichloride, dicyclopentadienyl hafnium chloride, dicyclopentadienyl hafnium dicarbonyl, dicyclopentadienyl hafnium dimethyl, bis-(methyl-cyclopentadienyl) hafnium dibromide and the like.

In general, any prior art technique for metal plating an object by thermal decomposition of a metal-containing compound can be employed in the present plating process as long as a cyclopentadienyl group IV-B coordination compound is employed as the plating agent (i.e., the metallic source for the metal plate). For example, any technique heretofore known for the thermal decomposition and subsequent plating of metals from the corresponding metal carbonyl can be employed. Illustrative are those techniques described by Lander and Germer, American Institute of Mining and Metallurgical Engineers, Technical Publication No. 2259 (1947). Usually, the technique to be employed comprises heating the object to be plated to a temperature above the decomposition temperature of a metal-containing compound and thereafter contacting the metal-containing compound with the heated object. The following examples are more fully illustrative of the process of this invention.

In Examples I-IV the following technique is used:

Into a conventional heating cham'ber housed in a resistance furnace and provided with means for gas inlet and outlet, is placed the object to be plated. The organometallic plating agent is placed in a standard vaporization chamber provided with heating means, said vaporization chamber being connected through an outlet port to the aforesaid combustion chamber inlet means.

For the plating operation, the object to be plated is heated to a temperature above the decomposition temperature of the organometallic plating agent, the system is evacuated and the organometallic compound is heated to an appropriate temperature where it possesses vapor pressure of up to about millimeters. In most instances, the process is conducted at no lower than 0.01 mm. pressure. The organometallic vapors are pulled through the system as the vacuum pump operates; and they impinge on the heated object, decomposing and forming the metallic coating. In most instances, no carrier gas was employed; however, in certain cases, a carrier gas can be employed to increase the efficiency of the above disclosed plating system. In those cases where a carrier gas is employed, a system such as described by Lander and Germer, page 7, is utilized.

Example I Compound (C H TiCl Substrate temp 575 C. Substrate Pyrex fibers. Pressure 0.15 mm. Compound temp 225 C. Time (hours) 2. Result Shiny, metallic coating.

4. Example II COIHPOUIJCI Substrate temp 575 C. Substrate Graphite. Pressure 0.3 mm. Compound temp 190 C. Time (hours) 3. Result Grey coating. Example III Compound (C H ZrCl Substrate temp 555 C. Substrate Pyrex fibers. Pressure 4.0 mm. Compound temp C. Time (hours) 2. Result Shiny, metallic coating. Example IV Compound (C H ZrCl Substrate temp 550 C. Substrate Copper mesh. Pressure 0.2 mm. Compound temp 190 C. Time (hours) 2. Result Shiny, metallic coating.

In the above examples, the temperatures utilized (i.e., in the vicinity of 500-585" C.) gave excellent metal plates. The process employed resistance heating. In the following working examples an induction heating method, using higher temperatures (i.e., greater than 650 C.) was employed. In the latter process, titanium and zirconium carbide coatings of excellent characteristics were obtained as opposed to the metallic coatings obtained in the foregoing examples.

The process employed in these examples is essentially the same as that employed in Examples I through IV with the exception that the object to be plated was placed into a conventional heating chamber provided with means for high frequency induction heating as opposed to the former process where the heating chamber was housed in a resistance furnace.

Example V Compound (C H TiCl Substrate temp 650-700 C.

Substrate Mild steel.

Pressure 1.0 mm.

Compound temp C.

Time (hours) 3.

Result Dark, shiny, hard, welladherent coating.

Example VI Compound (C H ZrCl Substrate temp 650700 C.

Substrate Mild steel.

Pressure 0.5 mm.

Compound temp 170 C.

Time (hours) 3.

Result Dark, shiny, hard, welladherent coating.

It is therefore seen, by comparing the above groups of working examples, that the process of this invention is highly novel in that by varying the temperatures of the decomposition it is possible to produce either a pure metla plate or a carbide coating, as one desires.

In addition to the thermal techniques disclosed hereinabove for decomposing the group IV-B plating agents of this invention, other methods for decomposition of these materials can be employed. Thus, the following working example is illustrative of the decomposition of a titanium compound by ultrasonic frequency.

The process employed in Example V and VI is followed with the exception that an ultrasonic generator is proximately positioned to the plating apparatus. In this example the compound was heated to its decomposition threshold, i.e. in the vicinity of 90 C. and thereafter the ultrasonic generator was utilized to eifect final decomposition.

Example VII Method Thermal and ultrasonic decomp. Compound (C H Ti(CO) Compound temp 100 C.

Substrate Pyrex fibers.

Substrate temp 200 C.

Pressure 1 mm.

Result Metallic coating.

Another method for decomposing the plating agent of this invention is by decomposition with ultraviolet irradiation. The following example is illustrative of this technique.

The method of Example I was employed, with the exception that, in place of the resistance furnace, there was utilized for heating a battery of ultraviolet and infrared lamps placed circumferentially around the outside of the heating chamber. The substrate to be heated was brought to a temperature just below the decomposition temperature of the plating agent with the infrared heating and, thereafter, decomposition was effected with ultraviolet rays.

Exam ple VIII Method Thermal and ultraviolet decomp. Compound (C H TiBr Compound temp 160 C.

Substrate Aluminum.

Substrate temp 400 C.

Pressure 1 mm.

Result Light metallic coating.

The term substrate, as employed herein-before, can be defined further as the object to be plated and includes any material stable at the temperatures necessary for decomposition of the group IV-B transition metal coordination plating agent employed. Thus, this invention is applicable to plating or coating of Pyrex glass and spun glass; various synthetic fibers and plastics such as polytetrafiuoroethylene, polychlorotrifiuoroethylene, rayon, nylon, Belrin (polyformaldehyde resin) and the like; steel such as nickel plated steel, mild steel, nickel plated mild steel; metallic turnings such as copper, zinc, and the like; cellulose materials such as cotton, wool, and the like in short, any materials stable under the plating conditions employed.

It should be noted that when employing the novel organometallic plating agents of this invention, it is necessary to maintain enough vapor pressure, below the decomposition temperature of the organometallic, to enable the process to be conducted at an appreciable rate of plating. Too high vapor pressure results in somewhat inferior substrate adherence. Thus, it is preferred to employ up to about mm. pressure during the plating operation-preferably 0.01 to 10 mm. pressure.

As has already been pointed out, temperatures are very important in obtaining the desired plated product. Thus, although temperatures above the decomposition temperature of the dicyclopentadienyl metal coordination compound can, in general, be employed in the plating process of this invention, best results have been attained within certain preferred temperature ranges. For example, temperatures ranging from about 500 C. to about 585 C. produce relatively pure metal plated products and temperatures in the range of about 650 C., or above, produce carbide-containing products when the chlorides of the dicyclopentadienyl titanium compounds are employed. The plating compounds of the present invention vary insofar as their thermal stability is concerned, but all of them can be decomposed at a temperature above 400 C., and

some as low as 100 C. Generally, decomposition occurs above 500 C. when employing chloride derivatives of the group IV-B cyclopentadienyl transition metal composition. Other materials, such as the bromides, decompose at lower temperatures (e.g. about 400 C.). The maximum temperatures which are employed are around 700 to 750 C.

Other examples illustrative of this invention follow:

of dicyclopentadienyl group IV-B coordination compounds containing difierent metals are employed in the plating process to produce alloys of the respective metals upon appropriate substrates. An example of this embodiment is the utilization of dicyclopentadienyl titanium dichloride and dicyclopentadienyl zirconium dichloride as plating agents in a process similar to that used in Examples I-IV. The following example more fully demonstrates this embodiment.

Example XI Method Thermal decomposition as in Ex. I. Composition An equimolar mixture of dicyclopentadienyl titanium dichloride and dicyclopentadienyl zirconium dichloride.

Composition temp 175 C.

Substrate Aluminum.

Time (hours) 2.

Substrate temp 575 C.

Pressure 0.5 mm.

Result Metallic coating.

The cyclopentadienyl substituents of the group IV-B transition coordination compounds employed as plating agents in this invention have previously been defined as substituted or unsubstituted cyclopentadienyl moieties. More specifically, these moieties have been defined as cyclopentadienyl moieties containing a five carbon ring similar to that contained in cyclopentadienyl itself. In most cases the cyclopentadienyl moiety contains from 5 to about 15 carbon atoms. Illustrative of these cyclopentadienyl moieties are cyclopentadienyl, l-methyl cyclopentadienyl, 2-(o-tolyl)-cyclopentadienyl, indenyl, 2- methyl-indenyl, 3-phenyl-indenyl, fluorenyl, 3-ethy1- fluorenyl, 2-m-tolyl-fluoroenyl, and the like cyclopentadienyl containing moieties. The cyclopentadienyl radicals can alternatively be considered as a cyclomatic radical such as 4,5,6,7-tetrahydroindenyl, 1,2,3,4,5,6,7,8-octahydrofluorenyl, 3-methy1-4,5,6,7-tetrahydroindenyl, and 2- ethyl-3-phenyl-3,4,5,6,7-tetrahydroindenyl.

The constituents represented by Q in the above formula are electron donating groups capable of coordinating with the group IV-B metal atom in the compounds which are employed as plating agents in the process of this invention. Thus the groups represented by Q in the above formula are capable of sharing electrons with the metal atom so that the metal achieves a more stable structure by virtue of such added electrons. These electron donating groups in coordination with the metal are, generally, either organic radicals or molecular species which contain labile electrons. These electrons assume a more stable configuration in the molecule when associated with the metal. The electron donating group represented by Q may also be inorganic entities which are capable of existing as ions, such as hydrogen, the cyanide group, and the various halogens. In general, the electron donating groups represented by Q are capable of donating from 1 to 4 electrons. The halogens are representative of electron donating groups donating one electron and carbonyl illustrative of an entity donating two electrons. An entity donating three electrons is represented by the nitrosyl group and aliphatic diolefins are illustrative of entities capable of donating four electrons. In those compounds which are preferred plating agents in the process of this invention, Q represents electron donating entities capable of donating one or two electrons. Such entities are the halides such as chlorine, bromine, fluorine, iodine, and the like; alkyl or aryl hydrocarbons containing between about one and carbon atoms such as methyl, ethyl, propyl, n-octyl, n-decyl, phenyl, benzyl, and the like; the carbonyl group; and alkoxy and aryloxy groups. Of these it is most preferred that Q be chlorine, bromine, carbonyl, methyl, phenyl, butoxy, ethoxy, and methoxy groups.

The group IV-B metals which form the metallic constituent of a coordination compound of this invention include the metals titanium, zirconium and hafnium. Of these, titanium and zirconium are preferred because of their greater availability and excellent chemical and refractory properties. The most preferred metal is titanium because of its wide adaptability to a multitude of uses.

The following compounds more fully illustrate the types of group IVB transition metal coordination compound which can be employed as plating agents in this invention. These compounds are bis-(methyl cyclopentadienyl)titanium dichloride, bis-(methyl cyclopentadienyl)titanium dibromide, bis- (methyl cyclopentadienyl) titanium difluoride, bis (methyl cyclopentadienyDtitanium diiodide, bis-(methyl cyclopentadienyl)- titanium diastatide, and the corresponding metal halide compounds containing ethyl cyclopentadienyl, butyl cyclopentadienyl, octyl cyclopentadienyl, dimethyl cyclopentadienyl, dihexyl cyclopentadienyl, vinyl cyclopentadienyl, ethynyl cyclopentadienyl, phenyl cyclopentadienyl, methylphenyl cyclopentadienyl, 'acetyl cyclopentadienyl, allyl cyclopentadienyl, 'benzyl cyclopentadienyl, tolyl cyclopentadienyl, and other like radicals. In addition to the aforementioned titanium compounds, the corresponding zirconium and hafnium compound can also be employed. Thus, other dicyclopentadienyl compounds are bis-(methyl-cyclopentadienyl)zirconium dichloride, bis (methyl cyclopentadienyl)zirconium dibromide, dicyclopentadienyl hafnium dichloride, dicyclopentadienyl hafnium dibromide and the like. Other compounds are bis-(methyl cyclopentadienyDfitanium dicarbonyl, dicyclopentadienyl zirconium dicarbonyl, dicyclopentadienyl hafnium dicarbonyl, bis-(dimethyl cyclopentadienyl)titanium dicarbonyl, bis-(phenyl cyclopentadienyl)zirconium dicarbonyl, and the corresponding compounds of titanium, zirconium and hafnium containing =butyl cyclopentadienyl, octyl cyclopentadienyl, dimethyl cyclopentadienyl, dihexyl cyclopentadienyl, vinyl cyclopentadienyl, allyl cyclopentadienyl and other like radicals. Compounds which contain only cyclopentadienyl groups are dicyclopentadienyl zirconium, dicyclopentadienyl hafnium, bis-(methyl cyclopentadienyl)titanium, bis-(allyl cyclopentadienyl)titanium and the like. Other compounds are bis-indenyl titanium dichloride, 'bis-indenyl zirconium dichloride, difluorenyl titanium dibromide, difiuorenyl zirconium difiuoride, bis-(2- methyl-indenyl) titanium, and the like. Any of the above compounds can be employed to plate their respective metallic substituent upon a multitude of substrates-employing any of the techniques described hereinbeforeby controlling the temperature of the plating operation so that temperatures above the decomposition temperature of the particular dicyclopentadienyl group IV-B coordination compound are employed.

The group IV-B metal platesparticularly titanium and zirconium plates-find a multitude of uses in the aircraft, missile and chemical processing industries. Thus, aircraft and missile components which require ultra high quality performance characteristics, such as resistr ance to high temperatures and to chemical attack, can

satisfactorily meet these requirements when coated with a group IV-B refractory according to the process of the instant invention. In the chemical processing industry, the group IV-B metal plates produced by the process of this invention find use in equipment subjected to high temperatures and chemical attack-as, for example, heat exchangers employed in such an environment. A very thin film of the metal plated on various substrates is sufficient for most applications. In some instances this film has a thickness on the order of only a few microns thickness. By employing the process described herein thicker plates can easily and economically be obtained, should such thickness be necessary for a particular application.

Another important use of the titanium plates produced herein is in the coating of aluminum cooking utensils. By virtue of such coating food does not stick to the utensil-thereby eliminating the necessity for cooking lubricant and the like.

Another use of the metal plates produced according to the process of this invention is in the plating of plastics. An example of such a use is the titanium plating of automotive interior plastic trim. By virute of such plating the serious problem encountered in automobile bodies stored for long periods of time, whereby vapor loss from the plastic deposits on car windows and Windshields, is simply and economically overcome.

We claim:

1. A process for plating a substrate with a group IVB transition metal comprising decomposing the vapors of a dicyclopentadienyl group IV-B transition metal coordination compound while in contact with said substrate Said compound containing, in addition to the cyclopentadienyl groups, at least one electron donor group capable of donating l to 4 electrons.

2. A process for plating a substrate with a group IV-B transition metal comprising heating the substrate to be plated to a temperature above the decomposition temperature of a dicyclopentadienyl group IV-B transition metal cordination compound, having in addition to the cyclopentadienyl groups, at least one electron donor group capable of donating l to 4 electrons, and contacting the vapors of said coordination compound with said heated substrate.

3. The process of claim 2 wherein said coordination compound is dicyclopentadienyl titanium dichloride.

4. The process of claim 2 wherein the said coordination compound is dicyclopentadienyl zirconium dichloride.

5. A process for plating a substrate with titanium which comprises decomposing the vapors of a dicyclopentadienyl titanium dihalide while in contact with said substrate.

6. A process for plating a substrate with a group IV-B transition metal which comprises decomposing the vapors of a dicyclopentadienyl carbonyl compound of a group IV-B metal while in contact with said substrate.

7. The process of claim 6 wherein said compound is dicyclopentadienyl titanium dicarbonyl.

8. A process for plating a steel substrate with titanium which comprises decomposing the vapors of a dicyclopentadienyl titanium dih'alide while in contact with said substrate.

9. A process for plating an aluminum substrate with titanium which comprises decomposing the vapors of a dicyclopentadienyl titanium diha-lide While in contact with said substrate.

10. A process for plating a carbonaceous substrate with a group IV-B transition metal which comprises decomposing the vapors of a dicyclopentadienyl group IV-B transition metal dihalide in contact with said substrate.

11. A process for plating a substrate which comprises decomposing the vapors of a dicyclopentadienyl group IV-B transition metal coordination compound while in contact with said substrate; said compound containing, in

addition to the cyclopentadienyl groups, at least one elec- 15 2,95 5,95 8

tron donor group selected from the group consisting of halides, alkyl hydrocarbons containing between about 1 and 10 carbon atoms, aryl hydrocarbons containing between about 1 and 10 carbon atoms, carbonyl, alkoxy groups containing between about 1 and 10 carbon atoms and aryloxy groups containing between about 1 and 10 carbon atoms.

References Cited in the file of this patent UNITED STATES PATENTS 2,508,509 Germer et a1. May 23, 1950 2,638,423 Davis et a1. May 12, 1953 2,690,980 Lander Oct. 5, 1954 2,898,235 Bullofi Aug. 4, 1959 Brown Oct. 11, 1960 

1. A PROCESS FOR PLATING A SUBSTRATE WITH A GROUP IV-B TRANSITION METAL COMPRISING DECOMPOSING THE VAPORS OF A DICYCLOPENDIENYL GROUP IV-B TRANSITION METAL COORDINATION COMPOUND WHILE IN CONTACT WITH SAID SUBSTRATE SAID COMPOUND CONTAINING, IN ADDITION TO THE CYCLOPENTADIENYL GROUPS, AT LEAST ONE ELECTRON DONOR GROUP CAPABLE OF DONATING 1 TO 4 ELECTRONS. 